Detailed explanation of the steps for setting element styles in js

This time I will bring you a detailed explanation of the steps for setting the element style in js. What are the precautions for setting the element style in js? The following is a practical case, let's take a look.

Many people don’t know how to set the element style when developing js. This article will bring you a js setting tutorial, so that everyone can better understand how to set up js. If you are interested, let’s take a look below.

When you see this title, the first thing you may think of is to use a routine like "[element].style.[css attribute name] = [attribute value]" to set the element style, but in fact, we actually have other ways to do it. choose.

Next, I'll detail three ways to style elements.

1. style

This is actually the method we are familiar with, for example~~

<p></p>

rrree This method seems simple and crude, but the writing method is too cumbersome, especially when a lot of styles need to be added. And it should be noted that CSS property names using dashes must be converted into camel case. (such as backgroundColor in the example)

2. style.cssText

This method is more concise than the above method, and is more like writing CSS directly on the element:

[Element].style.cssText = [CSS style];

For example:

var box = document.getElementById("box");
box.style.width = '100px';
box.style.height = '100px';
box.style.backgroundColor = "#f00";

Indeed, the writing method is very convenient.

However, the disadvantage is that styles added later in this way will overwrite the styles previously specified through the style attribute.

It’s the same example as above, but two pieces of JS are written together:

box.style.cssText = 'width: 200px; height: 200px; border: 1px solid #f00;';

If you follow the characteristics of the cascading style sheet, the red background color defined above should still exist. However, in fact, the style defined below through the style.cssText method will override all the styles added through the style (including style.cssText) method. Therefore, the final performance result of this example is the same as the one above when there is only one sentence.

Finally, please pay attention to compatibility. IE8 and earlier versions do not support cssText.

3. insertRule()

This usage is more complicated than the above two methods:

[sheet].insertRule([CSS style], specify location)

[sheet] represents a style sheet, which can be obtained through document.styleSheets. So, what are document.styleSheets? To put it simply, it means all style sheets applied in the document, including styles introduced through the link tag and styles defined by the style tag. If it’s still a bit difficult to understand, let’s give an example~~

First introduce the style sheet in the header:

var box = document.getElementById("box");
box.style.width = '100px';
box.style.height = '100px';
box.style.backgroundColor = "#f00";
box.style.cssText = 'width: 200px; height: 200px; border: 1px solid #f00;';

Of course, this style sheet must actually exist, and it doesn’t matter even if no styles are written in it. You can also use the style tag directly, and it doesn't matter if the content is empty.

Then use JS to get this style sheet:

<link>

Finally we can add styles to this style sheet:

var sheet = document.styleSheets[0];

The size is still 200*200, and the background color is green, which means that the width and height styles set by style.cssText overwrite the styles set by insertRule(). The reason is very simple. The styles set by style (including style.cssText) belong to Inline styles naturally have a higher priority than styles set by insertRule().

Priority~~

So, what does the second parameter 0 of insertRule() in the example refer to?

It refers to the location where we need to add CSS code, so parameter 0 represents the beginning of the style sheet.

For example, we first manually add a style to the style sheet (the following example has nothing to do with the above example):

sheet.insertRule('#box{width: 300px; height: 300px; background-color: #0f0;}',0);

<style>
  #box{ width: 100px; height: 100px;}
</style>

The result of the above execution is a green box with a width and height of 100*100:

If the second parameter in insertRule() is changed to 1, then the CSS code added through JS is equivalent to being added behind #box{ width: 100px; height: 100px;}, similar to the following:

var sheet = document.styleSheets[0];
sheet.insertRule('#box{width: 300px; height: 300px; background-color: #0f0;}',0);

It should also be noted that insertRule() is not compatible with IE8 and earlier versions, but you can use addRule() instead. The syntax is slightly different. The above example is written like this:

Copy code The code is as follows:

	sheet.addRule('#box','width: 300px; height: 300px; background-color: #0f0;',0);	

第一个参数代表元素，第二个参数代表CSS样式，第三个参数代表插入位置，前两个参数必选，最后一个可选，不填则默认为0。

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